This is a HT sub I call the VC1 it is short for Velocity Coupled after a design that I found a patent of in another forum.

the first thing I did was to take my existing KLH 10" 120W HT sub and add four strips of foam.

This is the foam I used. It is used to weatherproof windows and doors, but I'm using it as an airtight spacer so the woofer cone does not bump the Velocity baffle. The Velocity baffle is a thin piece of plywood that has a hole in it centered over the distcap of the woofer.

This is a sub box that was designed for a 12" polk audio or something. I can't remember, but the motor went to crap when the VC melted in two.

I added foam around the opening to seal it and also keep the Passive baffle from wrecking on the outside of the box. If I had money I would have replaced the woofer baffle the propper way.

this is what it looks like with the passive baffle in place on the passive enclosure.

You can't see the passive radiator in the back, yes this uses both a passive radiator and a slot port and is extremely efficient.

The tape is covering a tightly rolled piece of paper and holding it in place. The paper sharpens the inside edge of the hole as I don't have the proper tools to cut it at a 53 degree angle. It works anyway, but probably not as well as if I had all the tools.

this is the outside of the bed. This is all underneath a thick wooden top with a mattress on it. the mattress is removed right now until I can install the other hydraulic.

BTW this is inside the bedroom of my new 5th wheel trailer that I will be living in until I finish school. I'm going to have a degree in computer engineering when I'm done. YAY!!

this is a better shot of it.

The top is made from a nice piece of baltic birch 1/4" thick that accidentally got cut the wrong dimension. I couldn't find a use for it as a sub box cause it's just too thin, and the birtch is paper thin on the outsides of the cheapest plywood I've ever seen. looks nice as a bed though...

well I didn't make the pictures work I guess. Sorry, but no time to do anything about it. the library is closing in 20 mins.

About the box.

with the boxes in thier places the faces of the two boxes are more than 2 inches apart. The hole in the velocity baffle in front of the woofer had to be enlarged because it would fart and whistle with the described dimensions in the plans for a Graham Holliman Velocity Coupled Infrabass Subwoofer.

Yes there are both a slot port and a passive radiator in the passive enclosure. The active enclosure is what came with the KHL sub and is ported as well.

The sound is incredibly deep due to the fact that the hole that the passive radiator is activated with is 1/4 the size of the radiator itself. The PR is tuned to the exact frequency that the port is tuned to. but is only active with every other occilation due to the velocity coupling. this is because it takes one complete exhalation breath, while the cavity takes two. Does that make sense to you? the port keeps up with the cavity and resonates normally because the ends or it are the same area and there is no cone moving away from the throat with pressure increase and wasting time pushing it back through a hole when it is rarefacted.

It doesn't sound "loud". I could easily go to sleep with the totally natural sound of the bass with the amp at half gain. While my Aunt could hear it almost two blocks away in her van. ( went over like a lead baloon filled with sand bags!)

well the library is closing so I can't tell you more cause it's snowing in the Puget Sound and everybody is totally freaked about it. I don't know what the big deal is myself, but I grew up in Colorado.

TTYL

Please ask questions so I can think about them myself and come up with better stuff.

You have been messing with this Graham Holliman thing for a long time now. Have you per chance played with the "acoustic lever" idea any? I know the Holliman thing is supposed to extend the very low frequencies quite a great deal, but isn't so huge a break from the norm as far as efficiency. Acccording to the designer, the lever is a huge improvement, but isn't practical. I was thinking of playing with some of my computer speakers to see.

I have not been able to understand how the lever works. Do you have a link to the information on it? I seem to have lost some of my stuff cause I have pages missing.

The VC or Velocity coupling is VERY efficient. It is so much more efficient than the simple KLH sub it makes it seem puny and weak by comparison. It is basically doing the same thing as the chamber in front of a horn mouth of a midrange horn. I have figured it all out and it is basically loading the driver better and loading the chamber with pressurized air. The dimensions were off in the plans Holliman wrote out because the drivers that were available had almost nothing for xmax, but were highly efficient on one watt. Drivers have changed tremendously since 1950.

Imagine it like this. The hole in the velocity baffle infront of the driver is like adding a nozzle to a hose. Instead of just running out of the hose, the water is restricted just enough to spray violently. Using the same dimensions for a new 10 inch driver that you would have used for a 1950's driver is like trying to put a graden hose nozzle on a firehose pressurized by a pump on a firetruck. The nozzle would either desintegrate or the hose would explode. That's what was happeneing to the sound.

The VC sub is efficient and has good SQL because it has the right nozzle for the amount of flow. The amount of flow is controlled and dynamic if the hole in the baffle is the right size. This makes the passive box work efficiently and sound amazing because it is loaded by air not by a cone moving back and forth. The air that is loading it has 2.32 times the pressure than the air on the rear of the driver in the ported box has because it is being forced through a small hole. The rarefaction is 1.87 times as strong as the first pressurization. The pressure levels out at 3 cycles at 3.34 times more than the regular laoding. This makes the passive box louder than the active box by a total of 12.78 db by the time you add a port and passive radiator. Just enough to sound a little louder.

The VC sub is the deepest I've ever heard because the low cut-off is probably somewhere like 17 HZ. I don't have the software at the moment that is capable of measuring it, but that is what I guess based on what my keyboard sounds like. I can hear the deepest tones at the same level of the sound at 60hz.

The two boxes are not the only thing that makes the VC sub. The bed it is under which measures 92"X41"X17" is covered in carpet because it is the biggest part of the sub and makes the whole thing work. With the lid closed and the it's high Q port open it makes for one gigantic sub box. Quite possibly the largest I have ever made. It does not matter what I choose to store in under the bed because it actually makes the sound better. The port in the bed is at the top behind where the headboard will be. It resonates evenly across all frequencies because the length of the port is 0.

You should come over and play some Halo with me. When the big flood guys explode itls like popping an oxygen tank, and the doors feel like they weigh a ton.

I watched The Day After Tomorrow, I think, with all the storms and stuff and was amazed at the sound water makes when it floods a city in a 16 foot high wall. You can hear all kinds of things that you wouldn't normally hear. In King Arthur you can hear the deep plunk when a guy falls into the stream and later on it feels like the floor is breaking underneath you when the ice breaks under the saxons feet. the floor is literally moving enough to feel like it is falling away from underneath you and the pressure in your chest is exciting.

I have never felt or heard anything like this. Holliman knew what he was doing. I just tweaked it to work with modern equipment in a practical and effective way. My current build was aimed at efficiency and not low frequency as much because the lows were going to be there no matter what. I still need to work on it, but the sub is seamless with my mains and you wouldn't really know that my sub even exists. It just seems like the room comes alive with the movie or game. My mains could be better, but then again they cost $20.00! Somehow they dissappear when used in conjunction with the sub and my Sound Blaster live though.

Well I'm going to look around at some other posts. Let me know if you want to know more about something.

Glad to see you got it working so well Hellion. That is one awesome peice of tenacity. If I ever manage to find the time, I will probably play with this design a bit too. I like the idea of using the passive box to extend frequency and efficiency. In effect the acoustic lever isn't far from this design really. The ideal is a small woofer in a sealed cabinet firing into a cabinet with a passive radiator, firing into a cabinet with a larger passive radiator. I believe the reason it isn't considered practical is vessel pressure. The holliman idea takes away the problem of pressure by not using a passive (by itself) to radiate the sound out of the enclosure.

I have always thought the best efficiency would be to compress the drive unit in such a way that it forces more sound out of the enclosure, but getting it to tune to any more than one note seemed a daunting task. Glad to see this works. It means there is hope for some of the ideas that have been laid to rest without thorough investigation.

I remember this discussion as well. I Never gave it much credence but found it interesting but considering the time needed to invest in it I completely left it. I don't have time anymore to do the simplest stuff let alone start experimenting again. It does fascinate me and hopefully Hellion will have it all figured out. Glad you stuck with it and found something that works for you nice to stop by and hear about it. I look forward to seeing some pictures.Have a good one.